[CM30]

For most CSS and JavaScript incompatibility issues, the way to check doesn't require UA sniffing at all. You merely check if the browser supports said feature by looking for whether the supports media query runs or if the new method is available at all.

https://developer.mozilla.org/en-US/docs/Web/CSS/@supports

[silverwind]

@supports is often unreliable for CSS features. At least in Blink, it acts more as a "valid syntax" check then a "supported feature" check and for some reason Blink's CSS engine recognizes many new CSS features as valid syntax while not actually supporting them.